| Summary: | 碩士 === 國立臺北科技大學 === 能源與冷凍空調工程系 === 107 === This research established an evaporative cooling test system using elliptic tubes. Tests were conducted at various air volume flow rates (52、68、81、96 CMM), spray water flow rates(40、50LPM), using two types of water-spraying nozzle (A type, and B type) at several external air temperatures (TWB,i =18、22、25 ℃). The tube side hot water flow rate were fixed at 28, 22, or 18 LPM. The convective heat transfer of the spray water film outside the tubes and the heat and mass transfer between air and water film on tube bundles were investigated.
The results show that the heat-mass transfer performance of the evaporative cooler was enhanced with the increasing of air volume. When the spray water flow rate was risen to 50 LPM, the heat-mass transfer coefficient of the evaporative cooler decreased because the water film on the tube was too thick. At the same spray water flow rate, the two water-spraying nozzles yielded different spray water distribution, resulting in different water film thickness on the tube array and the heat and mass transfer performance. At a high air wet bulb temperature (TWB,i = 25 ℃), the overall performance of the evaporative cooler was better because of favorable physical properties of air-steam mixture. Low tube side water flow rate (18 LPM) results in high water inlet temperature, and consequently results in high spray water temperature on the upper half of the tube array, and higher overall performance of the evaporative cooler. From the experimental results, correlations for the water film heat transfer coefficient and air-water mass transfer coefficient are developed. They predict the present data within 15%.
|
|---|
